Telephone system.



E. P. W. ALEXANDERSON.

TELEPHONE SY$TEM.

APPLIOATION FILED APR. 14, 1913.

Patented July 7, 1914.

3 SHEETSSHBET 1.

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WITNESZE'S f/v YENTUH 2' M I EHNSTF WALEXANDERSDAZL, W M9,,

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E. P. W. ALEXANDERSON.

TELEPHONE SYSTEM.

APPLIOATIOK FILED APR.14, 191s.

Patented July 7, 1914.

3 SHEETSSHEET 2.

WZ'TNESSES. JNVENTUR.

E. F. W. ALEXANDERSON.

TELEPHONE SYSTEM.

APPLICATION FILED APR. 14, 1913.

Patented July 7, 1914.

3 S HEETSSHEIBT 3.

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Hrs ,Arrazazvax UNITED OFFICE.

ERNST F. w. nrnxnnnnns on, oF SonEnncrAnY, new YORK, Assicnon T0 GENERAL ELECTRIC COMPANY, A oonrona'rron or new YORK.

Specification, of Letters Patent.

rnnnrnonn SYSTEM.

Patented July 7, 1914.

' Application filed April 14, 1913. Serial No. 760,976.

apart.

More particularly, my invention relates to multiplex telephony systems in which it is necessary to transmit the telephone currents over long distances.

The principal problem, heretofore, in the development of a system of telephony and particularly a multiplex telephony system, using tuned alternating current circuits, has been the transmission of high frequency alternating currents over long distances. I have described in Patent No. 996,445, granted July 27, 1911, a system of telephony in which a high frequency alternator is employed as a telephone relay to' amplify or reinforce telephone currents. I have found by experiment that in such a system employing frequencies above 10,000 cycles no disturbance is produced in the telephone message, while with frequencies as low as 6,000 cycles the disturbance producedis so great that the message can scarcely be understood. Telephone lines are usually constructed for frequencies considerably lower than those mentioned, and it is very desirable to employ, if possible, these lower frequencies. Tothis end, my invention contemplates a system of transmission in which relatively low frequencies may be employed and in which the usual disadvantages of these frequencies are avoided.

W hen a single phase alternating current is rectified a unidirectional current is produced having a pulsation Witha'frequency twice that of the fundamental alternating current. If a quarterphase alternating current is rectified the rectified current has a pulsation with a frequency four times the frequency of the. fundamental current, and if a three phase current is rectified, the

" pulsation of the rectified current has a he quency six times as great as the frequency of the fundamental current. Furthermore, the amplitude of pulsation is decreased as scribers circuit.

the number of phases is increased. With three phase transmission a frequency of 3,000 cycles can, therefore, be employed to transmit a telephone message as satisfactorily as a single. phase current of 9,000 cycles.

The object of my invention is accordingly I to proyide' a telephone system in which the telephone currents are amplified and transmitted as polyphase alternating currents.

A further object of my invention is. to provide a system of multiplex telephony employing polyphase alternating currents for the effective transmission of the telephone currents from one station to another.

My invention consists in the use of a polyphase alternator as a relay in'a telephone system, together with means for the polyphase transmission of the 1 telephone currents between the calling and the answering stations. I preferably provide a plurality ofpolyphase alternators of different. fre- -quenc1es at each central exchange. Each of operation thereof will be-understood by reference to the following description taken in connection with the accompanying drawings, in which:

Figure 1 is a diagrammatic explanatory View of one embodiment of myinvention; Fig. 2is a diagrammatic view of theembodiment of my invention shown inFig. 1 with the necessary apparatus for transmit ting andreceiving telephone messagesbetween two stations; Fig. 3 is a diagrammatic view of a multiplex system of telephony, embodying the features of my invention; Fig. 4. is another modification of my invention; and Fig. 5 is an explanatory view.

The principle of operation of my inven- I also provide at each cen- I erence to 1 of the drawings. In this figure, I have represented diagrammatically thestator winding of a polyphase alternator 6. This alternator is preferably of the inductor type having a single winding serving as both a field and armature winding and an inductor arranged to rotate at high speed.- Each phase of the stator winding of the alternator comprises a plurality of sections 7. All the sections of the winding are connected in series with respect to the transmitting circuit which includes a source of direct current 8 and a transmitter or microphone 9.

The sections 7 of each phase of the alternator winding are connected in parallel with respect to an 'eiiternal circuit, which supplies current to the primary winding 10 of a polyphase transformer. Each phase of the primary winding of the transformer consists of a plurality of sections 11, and these sections are connected in parallel with respect to the winding of the alternator by means of conductors 57 and conductors 57. The sections 11 are, furthermore, connected in series with respect to the transmitting circuit by means of conductors 57 The pulsating telephone current. flowing through the sections 7 of the winding of the alternator will cause, by the rotation of the inductor of the alternator, an amplified or reinforced polyphase alternating current of. predetermined frequency to be induced in the winding. This current will be transmittedv as a polyphase current to the primary winding 10 of the transformer. The connection of the sections 7 of the winding of the alternator in series with the transmitting circuit and the similar connection of the sections .11 of the primary winding 10 of the transformer provide an arrangement in which the alternating voltages induced in or impressed oIi the sections of each phase of these windings are in opposition and hence neutralize each other in the transmitting circuit. The parallel connections of the sections 7 and 11 of each phase of th alternator and transformer windings respectively permit the effective utilization in an external circuit of the currents induced in the winding of the alternator.

A secondary winding 12 is arranged in operative relation with the primary winding 10 and is connected by polyphase transmission conductors 13 to a primary winding'14 of a transformer at the answering station. The secondary. winding 15 of this trans"- former is operatively connected to the terminals. of a polyphase rectifying device 16 which acts as a detector for the alternating current flowing in the transmission. conductors. In this figure I have illustrated a mercury vapor rectifying device of well known constrpction. A starting circuit 17 -ofthe usual type is provided in conjunction with i ductor 20 connected to the neutral point of the secondary winding 15.

The operation of the system diagrammatically illustrated in Fig. -1 will, it is believed, be obvious from the foregoing description. The pulsating telephone current produced in the transmitting circuit by speaking into the transmitter 9 flows through the stator winding of the alternator 6 and causes to be induced in this winding a polyphase alternating current of a definite frequency. This polyphase alternating current is sent out over the polyphase transmission conductors 13 at relatively high voltage by means of the sending transformer, and is rectified by means of the -polyphase current rectifying device 16. A unidirectional current, therefore, flows through the receiving circuit producing the usual sound waves in the receiver 18.

The character of tlie unidirectional cur- .rent is shown in Fig. 5. This figure shows Fig. 20f the drawings. In this figure, I

have shown two stations A and B. The

transmitting circuit of each station includes 1 the battery 8 and transmitter 9, and is connected to the stator winding of the alternator 6 and the primary winding lOof' the sending transformer in the same manner as described in connection with Fig. '1. The secondary-winding 12 of each sendingtransformer is connected through tuning instrumentalities 21 to the polyphase transmission conductors 13. The primary windings 14c of the receiving transformers at each station are connected through similar tuning instrumentalities tothe transmission conductors. The alternators thus act as'relays or amplifiers for the telephone currentsfiowing in the transmittingcircuits of their respective stations. The telephone currents, when A thus amplified, are sent out over the transmisslon conductors 13 as mg currents.

polyphase alternat- The alternator at the station A is designed I to generate a current of di'fierent frequency from that generated bythe alternator at the station B. The tuning instrumentalities 21,

n operative relation with the primary wind- I ing 14 of the receiving transformer at each station, will be tuned to receive currents of the frequency generated by the alternator at the other station.

tin circuit at station B will be amplified and sent out over the transmission conductors 13, detected and rectified, and sent through the receiving circuit of the station.

A. At the same time and without interference, the telephone current in the transmit ting circuit of station A will be amplified, I

sent out over the transmission conductors 13,

detected and rectified, and passed throughthe receiving circuit of the station E.

In Fig. 3, I have shown diagrammatically the application of my invention to multiplex telephony. I have shown in this figure only one central exchange, but it will be understood that the arrangement of the apparatus at the other central exchange is precisely the same as that shown for the exchange illustrated. In Fig. 3 I have repto polyphase bus bars 26 through tuning instrumentalities 27. The alternator 25 is connected through tuning instrumentalities 28 to the polyphase bus bars 29. The tuning instrumentalities 27 and 28 may, obviously, be omitted if desired. When employed they serve to tune the sending circuit so that this circuit can be given a minimum impedance corresponding to the frequency of the sending alternator. The bus bars 26 and 29 are connected to polyphase transmission conductors 30 through microphone relays 31 and 32 respectively. The microphone relays are of the usual construction and comprise a variable resistance arranged to vary in proportion to the strength of the current flowing in a-e'cooperating relay coil. The bus bars 26 and 29 are also connected to polyphase transmission conductors 59 through similar microphone relays 33 and 34 respectively. The terminals 35 of. the transmitting circuit of subscriber C' are arranged to be electrically connected to any pair of cooperating contacts 36, so that this transmitting circuit may be operatively connected to the microphone relay 31,32,

33 or 34. The transmitting circuit of the subscriber D is similarly provided with terminals 37 whichare arranged to be electrically connected to'any pair of cooperatlng contacts 38. The connection indicated by In this manner the telephone current flowing in the transmitdotted lines in thedrawings is such that the I transmitting circuit of subscriber C is operatively connected to relay 31, and the transmitting circuit of subscriber D- is operatively connected to relay 32.

A plurality of polyphase current rectifying detectors are located at the central exchange and each detector is arranged to be operatively connected to the receiving circuit of any subscriber. In the drawings I have illustrated vacuum valve rectifying devices of well known construction. These vacuum valve rectifiers comprise anevacuated chamber 39 in which is arranged a cathode wire 40 adapted to be maintained .in a highly heated or incandescent'state by a source of'direct current 41. An anode plate 42 and a grid 43' are arranged within each vacuum chamber. For the rectification of three phase currents three vacuum valve devices are necessary one devicebeing operatively related to each phase. These devices are connected in series in the receiving circuit, as indicated in the drawings, through terminals leading to the cathode wire 40 and the anode plate 42. The grids 43 within each vacuum chamber are operatively connected to secondary windings 44, which are operatively related to primary windings 45 arranged for connection through tuning instrumentalities 46, to either of the polyphase transmission conductors 30 or 59. The polyphase current rectifying detectors are arranged for connection to either of the transmission conductors through the switch 47. The receiving circuit of subscriber C is further provided with a switch 48 which permits either 'of the rectifying detectors to be operativelyconnected in this circuit. The receiving circult of the subscriber I) is similarly provided .with a switch 49'. As indicated by the dotted line connections in the drawings, the receiving circuit of subscriber G'is operatively connected through the left hand rectifying detector to the polyphase transmission conductors 30, and the receiving circuit of subscriber D is connected through the right hand rectifying detector to the same transmission conductors. source of direct current 50 is provided in connection with each rectifying detector,

and the pulsations of the current flowing through the receiving circuit vary in direct proportion to the amplitude of the currents flowing in the primary winding 45 of the transformer operatively connected to the rectifying detector.- This is accomplished by the effect of the electrostatic charge on the grids upon'the conductivity of the evacuated chamber 39.

The operation of the multiplex system of telephony shown in Fig. 3 is as follows: The transmitting circuit of subscriber C is operatively connected to the transmission conalternator 24 and microphone relay SL. The

magnitude of the current sent out over the transmission conductors from the alternator 24 will, therefore, be varied directly as the pulsations of the telephone current. Similarly the current in the transmitting circuit of subscriber D will be sent out over the same transmission conductors through the cooperation of the alternator 25, and microphone relay 32. As the alternators 24 and 25 generate currents of different frequencies, there will be no interference of these currents in the transmission conductors. At the receiving exchange rectifying detectors tuned respectively to selectively receive currents of a frequency corresponding to alternator-24 and alternator 25 will be provided, and these currents will be directed to: the receiving circuits ofthe answering subscribers, as described in the next paragraph in connection with the calling subscribers. v

As previously stated,- o'nly one :central exchange isillustrated in Fig. 3 'of the drjaw-v "ings, since the other exchangeis exactly the same as the exchange E. That is'the bus bars 26 and 29 are connected by transmission conductors to two similar sets of bus bars in the other exchange, and the apparatus of the other exchange and of-the subscribers stations are related to these latter bus bars in the same way as heretofore explained in connection with the exchange E. Thus, the reception at the other exchange of a message sent from the exchange E can be readily excircuitof subscriber O is connected through plained and understood by assuming that the message or messages are coming from the-other exchange and are being received- Assumlng a receiving at the exchange E. message for each subscriber, the receivlng the polyphase rectifying detector at the left I in the figure to the transmission conductors 30, and thereceiving circuit of subscriber D is connected through the right hand rectify- -ing detector to the same transmission con+- ductors. The tuning instrumentalities 46% of these rectifying detectors will be tuned to selectively receive currents corresponding to the frequency of the relay employed at the answering exchange and operatively connected to the transmitting circuit of the answer different frequencies, whereby no interferingsubscriber'. The sending and receiving currents of'each subscriber are preferably of ence is occasioned between these two currents in the transmitting and receivingapparatus of the two talkingsubscribers. Thus while subscriber C is sending messages with a current having a frequency corresponding to the frequency of alternator 24, he is receiving messages by a current of a different frequency determined by the frequency of the sending alternator at the other exchange.-

nator 51.

Similarly, the frequencyiof the alternator 2 5 with which subscriber D is sending messages is different than the frequency of the alternator at the other exchange by which messages are sent to the subscriber D. It will thus be seen that the transmission conductors 30 are carrying alternating currents of four different frequencies and that these currents are directed to their proper paths by means of, tuned circuits.

In Fig. 4 of the drawings I have illustrated a modified type of relay to beemployed in the transmitting circuit. In this figure, a polyphase alternator 51 is openatively connected to the transmission conductors 52. Transformer coils 53 are included in series with each transmission conductor. Operatively related to each pair of transformer coils 53 are transformer coils 54. The coiiperating transformer coils 54 of each pair are connected in opposition so that the voltages induced in the coils. 54 will be effect. All of the coils 54 are connected in series in the transmitting circuit which includes a source of direct current 55 and a microphone transmitter 56. In this type of relay the pulsating telephone currents will This magoperating transformer coils 53 and hence the magnitude of the currents sent out over the transmission conductors 52 from the alter- The receiving apparatus shown in Fig. 4 is of the same type as that described in connection with Figs. land 2. It will be understood, of course, that an answering station having a'similar arrangement of apparatus as that shown. in Fig. 4 will be'provided.

This answering station has been omitted in order to simplify the drawings.

description that I have provided a system nating currentsfor thetransmission of telephone currents from one station to another. The particular advantage in the use of poly.- phase currents is, as heretofore explained, that frequencies considerably lower than oppositein It Will ,be" evident from the foregoing V of telephony, making use of polyphase. alter- I those required withsingle phase currents can be employed. This is of decided advantage inasmuch asthe present telephone systerns are designed for lower frequencies than can be satisfactorily employed with single phase transmission. "I have in addition provided a system of multiplex telephony which makes use ofpolyphas'e alternating currents for simultaneously transmitting two or more telephone currents.

n will be obvious to those skilled in the art that my inventionmay be embodied in many difi'erent forms. and arran ements of apparatus than 4, that illustrate and derent.

nating current, means for rectifying said polyphase alternating current, and a receiving circuit adapted to carry the rectified our- 2. In a telephone system a transmitting circuit, a receiving circuit, a telephone relay comprising a polyphase alternator operatively connected to said transmitting circuit, a polyphase current rectifying detector operatively connected to said receiving circuit, and polyphase tra-nsmisison conductors between said relay and said rectifying detector.

3. In a multiplex telephony system, a plurality of transmitting circuits each adapted to carry a pulsating telephone current,

"means for producing a polyphase alternating current proportional to each of said telephone currents, each of said alternating currents so produced being of a different frequency, polyphase transmission conductors arranged to simultaneously carry all of said alternating currents, means for selectively rectifying each of said polyphase alternating currents, and a plurality of receiving circuits each adapted to carry a,

rectified current.

4:. In a telephone system, a plurality o subscribers circuits, a central exchange, a pluralityof telephone relays each comprising a polyphase alternator of different frequency, and means controlled at the central station for operatively connecting any relay to any subscribers circuit,

5. In a telephone system, acalling station and an answering station, each station having a transmitting circuit and a receiving circuit, a telephone relay comprising a polyphase alternator operatively connected to the transmitting circuit of each station, polyphase transmission conductors between said stations and operatively connected to said relays, and polyphase current rectifying detectors operatively connected to the receiving circuit of each station and to the transmission conductors.

6. In a telephone system, a subscribers circuit including a transmitting device and a receiving device, a second subscribers circuit also including a transmitting device other subscribers circuit.

and a receiving device, a telephone relay comprising a polyphase alternator operatively connected to each of said subscribers circuits, a polyphase rectifying detector opcratively connected to each of said subscribers circuits, polyphase transmission conductors electrically connecting the relay and rectifying detector in one subscribers circuit to the relay and rectifying detector in the other subscribers circuit, and means for tuning the circuit of the rectifying detector in each subscribers circuit for the frequency of the alternator of the relay in the .7. In a telephone system, a plurality of subscribers circuits in connection with a central exchange, a plurality of subscribers circuits in connection with a second central exchange, polyphase transmission conductors between said exchanges, a plurality of polyphase alternators' of different frequencies at, each exchange and arranged for operative connection as telephone relays to any subscribers circuit in connection with said exchange, a pluralityof polyphase current rectifying detectors at each exchange and arranged for connection to any subscribers circuit in connection with said exchange, and means for tuning the circuits of the rectifying detectors of one exchange for the frequencies of corresponding alternators of the other exchange.

8. In a telephone-system, a plurality of subscribers circuitsin connection with a central exchange, a plurality of subscribers circuits in connection with a'second central exchange, polyphase transmission conductors between'said exchanges, a plurality of polyphase alternators of different frequencies at each exchange and arranged for operative connection as telephone relays to any subscribers circuit. in connection with the latter subscribers exchange, a plurality of polyphase current rectifying detectors at each exchange and arranged for connection to any subscribers circuit in connection with the latter subscribers exchange, and means cooperating with said polyphase alternators and said polyphase current rectifying detectors for simultaneously connecting through said polyphase transmission conductors two or more of the subscribers circuits of one exchange in operative relation with a corre- ERNST nw. ALEXANDERSON.

Witnesses: I BENJAMIN B. How, HELEN ORF RD. 

